A prospective study will be undertaken concerning the immunologic response of children in whom the postpericardiotomy syndrome develops. The objectives are to (1) identify the pathogenesis of the syndrome, (2) learn whether there is a correlation between clinical manifestations and circulating antibodies against myocardium and certain viruses, (3) develop a specific diagnostic test, (4) determine optimal management and (5) if possible, prevent the complication. A pilot study by us on a double-blind basis in 60 children undergoing intrapericardial procedures indicated a correlation between the presence of syndrome, which occurred in 31% of subjects, and high titer of heart-reactive antibody determined by immunofluorescent technique. We propose to continue and to expand that study by an interdisciplinary approach. We shall evaluate at prescribed intervals clinical syndrome in the patient and concurrently measured serum antibody against myocardium and 12 specific viruses. Heart-reactive antibody will be determined by radioimmunologic as well as by immunofluorescent techniques for confirmation and for quantification of response. To test the possibility that cellular hypersensitivity to cardiac antigens might play a role in the syndrome, cellular studies will include migration-inhibition studies of peripheral blood lymphocytes and measurement of stimulation of DNA synthesis by sensitized lymphocytes, tested by incorporation of 14C thymidine. To characterize the heart-reactive antibody found in high titer, antibody eluted from an antigen-antibody aggregate will be tested as to immunoglobulin class and subtype and for the components of myocardial tissue against which it reacts, and it will be injected into primates to see if a syndrome develops analogous to that in man. Clinical management will be standardized and will not be altered until sufficient clinical, immunologic, and serologic data, independently obtained, has been collated to permit a judgment as to etiology and possible trial of therapeutic intervention or prevention.